The present invention relates to a retraction mechanism to remove a sensor assembly extending through a valve into a process fluid container from the process fluid container More particularly, the present invention provides a sensor retraction mechanism having a support linkage connected between the sensor assembly and the process fluid container with a damper to prevent uncontrolled ejection of the sensor assembly from the container when the container is under fluid pressure.
In order to measure properties of a fluid, such as conductivity, pH or temperature, a sensor usually must be placed in contact with the process fluid. The fluid can reside either in a process line or within a process container. Under most circumstances, the fluid is under pressure. It is sometimes desirable to install or remove the sensor without relieving the pressure of the process fluid. Typically, this procedure involves using a sensor assembly having a sensing element mounted on a long tube that extends through a gate or ball valve body connected to the fluid container. When the sensing element must be calibrated, replaced, inspected or cleaned, the tube and the sensing element as a unitare retracted through the gate or ball valve body until the end of the sensor assembly clears the valve element in the valve body. Then, the valve can be closed to keep the fluid under pressure, while the sensor assembly is removed completely from the valve to allow proper servicing.
If the sensor assembly is under pressure from the process fluid in the container, then when the sensor assembly is unlocked from the valve body, the sensor assembly is subjected to a force that tends to expel it from the valve body. Cables, chains, or lanyards have been connected to the sensor assembly to prevent the sensor assembly from accidentally ejecting from the valve body. Stop rings or flanges located near the end of the sensor assembly that contact opposed flanges or a tube fitting have also been used in an attempt to prevent the end of the sensor assembly from ejecting from the valve body.